in this AU, a zombie apocalypse broke out right after Sam's and Dean's mother had died so they had grown up killing monsters and zombies. At the beginning Angels fought to save mankind and even side by side with some demons. As time went by though, the battle was being lost and man kind turn they're backs on the angles and in a panic, hunted them. Using the wings of an angel in a ritual to heal one person from the zombie virus. Thus the Angels left vowing to never return again and they didn't. The worlds population was cut in half with in 3 nights and man kind realized their mistake. Many prayed for their return but no prayer was answered. heaven had closed their gates to man kind.
Years later, the world population had been spread into camps with everyone attempting to coexist and survive. Sam and Dean had become know as the worlds best monster and zombie slayers and are used for supply hunts by many of the camps. Strangely many people have begun to theorize that one of them are a last remaining angel left on earth, though they are far from the truth. Dean had made a deal with a demon to save Sam and had gone to hell only to miraculously return a year ago. While Sam had finally got off his demon blood addiction. though the tale of an angel that remains holds some truth. Castiel had rebelled against heaven and their leave, speaking on the behalf of man kind. Castiel held hope for the creatures that turned their back on them and remained on earth to continue the fight. But after years of fighting it had seem that god and heaven had forgotten him and the humans that remained.